The invention relates to a heat absorption conversion system, termed sorption system for short below, which is used in single- or multistage designs as a refrigeration machine, heat pump and heat transformer or combinations of these for the generation of cold and/or heat (G. Alefeld, R. Radermacher: Heat Conversion Systems, CRC Press, Boca Raton (1994)). Heat absorption conversion systems are also described in Niebergall, W: Handbuch der Kaltetechnik [Refrigeration Engineering Manual], Volume 7, Sorptionskaltemaschinen [Sorption Refrigeration Machines], Springer Berlin N.Y., reprint (1981), and in H. v. Cube, F. Steimle: Warmepumpen [heat pumps], VDI-Verlag Dusseldorf (1984). A critical factor for performance data of the sorption system is the sum of all reciprocal heat transfer coefficients at the main components used: evaporator, absorber, condenser, generator, desorper, resorber (P. Riesch, G. Alefeld, DKV-Tagungsberichte [Symposium Reports], Volume 17, Heidelberg, pp.569 ff (1990)). The absorber and resorber, in particular, require relatively large heat-exchange surfaces due to the poor mass transfer in absorption. In this case, turbulence in the solution is of great importance for thorough mixing of the solution and thus for the mass transfer and heat exchange in the absorber or resorber, just as in the case of boiling in the evaporator, generator or desorber. Turbulence in mass transfer and heat exchange is achieved by high energy exchange per unit area of heat exchanger, ie by high loads per unit area. Below, the generic term absorption heat exchanger is taken to mean diabatic, ie cooled absorbers and resorbers, such as trickle absorbers, also termed falling-film absorbers, equipped with, for example, tube-bundle or plate heat exchangers, immersion absorbers, also termed bubble absorbers, equipped with, for example, pipe-coil or plate heat exchangers, etc. (see, for example, Niebergall, W: Handbuch der Kaltetechnik [Refrigeration Engineering Manual], Volume 7, Sorptionskaltemaschinen [Sorption Refrigeration Machines], Springer Berlin N. Y., reprint (1981), pp. 379 ff).
It is known that the heat transfer in absorption heat exchangers may be enhanced, for example, by structured tubes (N. Isshiki, K. Ogawa, Proc. Munich Discussion Meeting on Absorption Heat Transfer Enhancement (1994)) or by additives, for example by Octanol (Y. Nagaoka et al., Proc. XVII Int. Congress of Refrigeration Vol.B. pp. 636, Vienna (1987)). A good discussion on heat transfer processes in absorbers is given in the subsequently published dissertation by F. Summerer (TU Munich, p.65, 1996). The heat transfer between solution and cooling medium does not generally limit the absorption process, however, this is limited by the mass transfer. A large heat exchange area in the absorber/resorber to improve the mass transfer by large surface area increases the costs of the absorber and creates wetting problems on the heat exchanger (J. Tang et al., 18th Int. Congress of Refrigeration, Montreal, p.519 (1991); I. Greiter, Dissertation TU Munich (1995), pp.36-37). Complete wetting of the heat exchanger is necessary for good heat transfer. In addition, for example with large heat-exchange areas or low input-heat temperatures and thus low energy exchange per unit of heat exchange area (load per unit area for short), the turbulence in the solution in the absorption heat exchanger and the effect of the additives which promote heat transfer decrease relatively sharply (K. J. Kim, Dissertation Arizona State University (1992), pp. 150). Low loads per unit area in the absorption heat exchanger also have an adverse effect on the loads per unit area in the other main components and can lead to relatively high specific heat exchange areas of the overall system and thus to high costs of the system.
It is further known, as already mentioned above, that, for example, the high exchange areas necessary at low input-heat temperatures in sorption systems having absorption heat exchangers, constructed, for example, as trickle absorbers, give rise to wetting problems. These problems are counteracted either with a decrease of the system efficiency by increasing the solution circulation rate between absorber and corresponding generator or else by recirculation at the absorber (H. v. Cube, F. Steimle: Warmepumpen [heat pumps], VDI-Verlag Dusseldorf (1984), p.195). In the case of recirculation at the absorber, the solution which, on account of the absorption limited by mass transfer, exits subcooled at the collector of the absorption heat exchanger, is pumped back to the distributor apparatus of the absorption heat exchanger. In particular, sorption systems of medium and small capacity equipped with absorption heat exchangers having a low tube-bundle height require high recirculation for complete wetting. With respect to as high a temperature level as possible for decoupling the heat of absorption and for heat transfer at the absorption heat exchanger, high recirculation has an adverse effect, since the driving temperature difference available for the heat transfer is decreased by the temperature difference between weak and strong solution (I. Greiter, Dissertation TU Munich (1995), pp.36-37).
A further known measure uncouples mass transfer and heat exchange in absorbers/resorbers by using adiabatic absorbers (W. A. Ryan, Proc. mnt. Absorption Heat Pump Conference, New Orleans, AES-Vol. 31, p.155, 1994)). As a result, the high surface area required for the mass transfer can be provided without requiring high heat-exchange areas. The heat exchange is carried out separately in a cooler in the recirculation circuit. A disadvantage in the case of adiabatic absorbers is that the heat of absorption leads on mass transfer to a relatively severe heating of the solution in the absorber, since the specific heat of absorption is very high in comparison with the specific heat capacity of the solution. This requires a high recirculation rate and/or intense subcooling of the solution and thus a high driving temperature difference between cooling water and absorption temperature in the adiabatic absorber with all the associated disadvantages, such as high input-heat temperatures, loss of temperature elevation, etc. (F. Summerer, Dissertation, TU Munich, p.83, 1996).
The abovedescribed measures for enhancing the absorption have in common the fact that the highest possible surface areas are provided for the mass transfer limiting the absorption. This is achieved by high absorption heat exchanger areas, eg. as tube bundles, or in adiabatic absorbers, eg. by packings.